Carrier-nanoparticle complex, preparation method therefor, and membrane electrode assembly including same

ABSTRACT

The present specification relates to a carrier-nanoparticle complex, a preparation method therefor, and a membrane electrode assembly including the same.

TECHNICAL FIELD

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0137015 filed in the Korean IntellectualProperty Office on Sep. 25, 2015, the entire contents of which areincorporated herein by reference.

The present specification relates to a carrier-nanoparticle complex, apreparation method therefor, and a membrane electrode assembly includingthe same.

BACKGROUND ART

Nanoparticles are particles having nanoscale particle sizes, and showoptical, electrical and magnetic properties completely different fromthose of bulk materials due to a large specific surface area and thequantum confinement effect, in which energy required for electrontransfer changes depending on the size of material. Accordingly, due tosuch properties, much interest has been concentrated on theapplicability of nanoparticles in the catalyst, electromagnetic,optical, medical fields, and the like. Nanoparticles may be consideredas intermediates between bulks and molecules, and may be synthesized interms of two approaches, that is, the “top-down” approach and the“bottom-up” approach.

Examples of a method for synthesizing a metal nanoparticle include amethod for reducing metal ions in a solution by using a reducing agent,a method for using gamma-rays, an electrochemical method, and the like,but in the existing methods, it is difficult to synthesize nanoparticleshaving a uniform size and shape, or it is difficult to economicallymass-produce high-quality nanoparticles for various reasons such asproblems of environmental contamination, high costs, and the like byusing organic solvents.

Meanwhile, [Nano Lett., 2011, 11(3), pp 919-926] describes a method forpreparing a core-shell particle including gold (Au) as a core andplatinum (Pt) as a shell, but only discloses a method for preparing acore-shell particle by using platinum (Pt)-acetylacetonate (Pt-(acac)₂),which is an organic metal compound, and an organic solvent, and does notdescribe a method for preparing a core-shell particle, which may solveenvironmental pollution and high cost problems.

Thus, there is a need for studies on preparing core-shell particlescapable of minimizing environmental pollution and being mass produced.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present specification has been made in an effort to provide acarrier-nanoparticle complex, a preparation method therefor, and amembrane electrode assembly including the same.

Technical Solution

An exemplary embodiment of the present specification provides a methodfor preparing a carrier-nanoparticle complex in which core-shellnanoparticles are supported on a carrier, the method including:preparing a carbon carrier having a portion or all of the surfacethereof coated with a polymer including a cationic functional group;forming core particles by reducing a solution including one or two ormore metal precursors, the carbon carrier, and a polyol at a temperatureof 120° C. or more and 220° C. or less to form metal core particlessupported on the carbon carrier; and forming core-shell nanoparticles byreducing an aqueous solution including metal core particles supported onthe carbon carrier, a Pt precursor, and water at a temperature of 20° C.or more and 100° C. or less to form a Pt shell on a portion or all ofthe metal core particle surface.

An exemplary embodiment of the present specification provides acarrier-nanoparticle complex prepared by the preparation method.

An exemplary embodiment of the present specification provides a membraneelectrode assembly including an electrode catalyst layer which includesthe carrier-nanoparticle complex and an electrolyte membrane.

An exemplary embodiment of the present specification provides a fuelcell including the membrane electrode assembly.

Advantageous Effects

A method for preparing a carrier-nanoparticle complex according to anexemplary embodiment of the present specification does not use anorganic solvent which is highly likely to cause environmentalpollutions, but uses an aqueous solvent, and thus has an advantage inthat there is little environmental pollution.

A method for preparing a carrier-nanoparticle complex according to anexemplary embodiment of the present specification can prepare acarrier-nanoparticle complex at high yield through a simple process.

The method for preparing a carrier-nanoparticle complex according to anexemplary embodiment of the present specification is carried out at alow temperature of 200° C. or less, and thus has an advantage in thatthe carrier-nanoparticle complex may be prepared in large amounts at alow cost.

A carrier-nanoparticle complex according to an exemplary embodiment ofthe present specification may implement high catalytic activity becausecore-shell nanoparticles with a uniform size are uniformly supported ona carrier.

The method for preparing a carrier-nanoparticle complex according to anexemplary embodiment of the present specification does not use asurfactant, and thus has an advantage in that hazardous materials aregenerated in small amounts in the preparation process, and thecarrier-nanoparticle complex may be easily formed at a low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an electron microscope photograph of Pd/Co coreparticles supported on a carbon carrier, which are prepared according toExample 1.

FIG. 2 illustrates an electron microscope photograph of acarrier-nanoparticle complex in which core-shell nanoparticles aresupported on the carbon carrier, which is prepared according to Example1.

FIG. 3 illustrates component analysis results of the core-shellnanoparticles of the carrier-nanoparticle complex, which is preparedaccording to Example 1, by using STEM EDS.

FIG. 4 illustrates an electron microscope photograph of Pd/Co coreparticles supported on a carbon carrier, which are prepared according toExample 2.

FIG. 5 illustrates an electron microscope photograph of acarrier-nanoparticle complex in which core-shell nanoparticles aresupported on the carbon carrier, which is prepared according to Example2.

FIG. 6 illustrates a current density-voltage graph of ComparativeExample 1, Example 1, and Example 2.

FIG. 7 is a normalization graph based on the amount of Pt per unit areain the graph in FIG. 6.

FIG. 8 illustrates a graph of the catalyst durability evaluationperformed by cyclic voltammetry in Example 1 and Comparative Example 1.

FIG. 9 illustrates XRD results of Example 2 and Reference Example 1.

FIG. 10 illustrates a current density-voltage graph of Reference Example2.

FIG. 11 illustrates component analysis results of the core-shellnanoparticles of the carrier-nanoparticle complex, which is preparedaccording to Comparative Example 2, by using STEM EDS.

BEST MODE

When one member is disposed “on” another member in the presentspecification, this includes not only a case where the one member isbrought into contact with another member, but also a case where stillanother member is present between the two members.

When one part “includes” one constituent element in the presentspecification, unless otherwise specifically described, this does notmean that another constituent element is excluded, but means thatanother constituent element may be further included.

Hereinafter, the present specification will be described in more detail.

An exemplary embodiment of the present specification provides a methodfor preparing a carrier-nanoparticle complex in which core-shellnanoparticles are supported on a carrier, the method including:preparing a carbon carrier having a portion or all of the surfacethereof coated with a polymer including a cationic functional group;forming core particles by reducing a solution including one or two ormore metal precursors, the carbon carrier, and a polyol at a temperatureof 120° C. or more and 220° C. or less to form metal core particlessupported on the carbon carrier; and forming core-shell nanoparticles byreducing an aqueous solution including metal core particles supported onthe carbon carrier, a Pt precursor, and water at a temperature of 20° C.or more and 100° C. or less to form a Pt shell on a portion or all ofthe metal core particle surface.

According to an exemplary embodiment of the present specification, thecore-shell nanoparticle may include a shell including Pt on at least aportion of a surface of a core particle including one or two or moremetals. Specifically, according to an exemplary embodiment of thepresent specification, the core-shell nanoparticle may include a shellincluding Pt on at least a portion of a surface of a core particleincluding two metals.

A precursor in the present specification means a salt including metalions. The precursor may be dissociated in a solvent to provide metalions, and the metal ion is reduced by a reducing agent, and thus maybecome a metal constituting the core-shell nanoparticle.

Preparing of Carbon Carrier

According to an exemplary embodiment of the present specification, thepreparing of the carbon carrier may include providing a carbon carrierhaving a portion or all of the surface thereof coated with a polymerincluding a cationic functional group.

According to an exemplary embodiment of the present specification, thepolymer including the cationic functional group may include one or morefunctional groups selected from the group consisting of an amine group,an imine group, and a phosphine group. The cationic functional group maybe a primary, secondary, tertiary, or quaternary functional group.

According to an exemplary embodiment of the present specification, thepolymer including the cationic functional group may be a polymer inwhich a straight or branched hydrocarbon chain is substituted with thecationic functional group.

Further, the skeleton of the polymer including the cationic functionalgroup may be a straight or branched hydrocarbon chain which does notinclude a cyclic molecule.

In the present specification, the hydrocarbon chain may be one or two ormore combinations of a saturated hydrocarbon and an unsaturatedhydrocarbon. For example, the straight or branched hydrocarbon chain maybe a straight or branched hydrocarbon chain in which carbon atomsbetween a saturated hydrocarbon and an unsaturated hydrocarbon arelinked in the form of straight or branched chains, or a straight orbranched hydrocarbon chain in which carbon atoms between a saturatedhydrocarbon and a saturated hydrocarbon are linked in the form ofstraight or branched chains.

According to an exemplary embodiment of the present specification, thepolymer including the cationic functional group may have a weightaverage molecular weight of 500 g/mol or more and 1,000,000 g/mol orless. Specifically, the polymer including the cationic functional groupmay have a weight average molecular weight of 1,000 g/mol or more and10,000 g/mol or less.

When the weight average molecular weight of the polymer including thecationic functional group satisfies the range, the carbon carrier iseasily coated, and the residual polymer after the coating is easilywashed.

According to an exemplary embodiment of the present specification, thepolymer including the cationic functional group may include one or moreselected from the group consisting of polyallylamine hydrochloride(PAH), polyethylene imine (PEI), and an allylamine amidesulfate polymer.The polymer may be branched.

According to an exemplary embodiment of the present specification, thecore-shell nanoparticles may form a bonding structure with the cationicfunctional group.

The cationic functional group may be bonded to the core-shellnanoparticles to alleviate aggregation of the core-shell nanoparticles,thereby increasing dispersibility of the core-shell nanoparticles.Furthermore, the N or P functional group of the cationic functionalgroup and the core-shell nanoparticles may be bonded to each other toform a composite of the polymer and the core-shell nanoparticles, andthe composite serves to increase the binding force of the carbon carrierand the core-shell nanoparticles, and may enhance durability of thecarrier-nanoparticle complex.

According to an exemplary embodiment of the present specification, thecarrier may be a carbon-based carrier.

Specifically, according to an exemplary embodiment of the presentspecification, the carbon-based carrier may include one or more selectedfrom the group consisting of carbon black, carbon nanotube (CNT),graphite, graphene, activated carbon, mesoporous carbon, carbon fiber,and carbon nano wire.

Forming of Core Particles

An exemplary embodiment of the present specification may include formingcore particles by reducing a solution including one or two or more metalprecursors, the carbon carrier, and a polyol at a temperature of 120° C.or more and 220° C. or less to form metal core particles supported onthe carbon carrier.

According to an exemplary embodiment of the present specification, thesolution may include one or two metal precursors.

The polyol means a polyhydric alcohol including two or more hydroxylgroups. Specifically, as the polyol, ethylene glycol, propylene glycol,and the like may be applied. However, the polyol is not limited thereto.

In the forming of the core particles, when a polyol is used as asolvent, there is an advantage in that core particles having a smallparticle diameter of 7 nm or less may be uniformly supported.

According to an exemplary embodiment of the present specification, themetal precursor may be ionized in a polyol.

According to an exemplary embodiment of the present specification, inthe forming of the core particles, the metal precursor may be aprecursor of one or more metals selected from the group consisting ofCo, Ni, Fe, Pd, Ru, Cr, and Cu.

According to an exemplary embodiment of the present specification, themetal precursor may be a precursor of two or more different metals.Specifically, the metal precursor may be a nitrate (NO₃ ⁻), a halide, ahydroxide (OH⁻) or a sulfate (SO₄ ⁻) of the metal.

According to an exemplary embodiment of the present specification, thehalide may be chloride (Cl⁻), bromide (Br⁻), or iodide (I⁻).

The content of the metal precursor may be appropriately adjustedaccording to the amount of core particles to be supported on thecarrier.

According to an exemplary embodiment of the present specification, theforming of the core particles may include adjusting pH of the solutionto 9 or more and 11 or less.

According to an exemplary embodiment of the present specification, inthe process of adjusting the pH, the pH may be adjusted by adding a basesolution. Specifically, the pH may be adjusted by adding a base solutionselected from the group consisting of sodium hydroxide (NaOH), bariumhydroxide (Ba(OH)₂), potassium hydroxide (KOH), calcium hydroxide(Ca(OH)₂), and lithium hydroxide (LiOH).

The metal core particles may be bonded to the cation of the polymerincluding the cationic functional group.

The preparation method according to an exemplary embodiment of thepresent specification has an advantage in that a process of supportingnanoparticles on a carrier is not separately needed. Specifically, sincethe forming of the core particles is performed by a one-pot process, aseparate supporting process is not needed. When a carrier-nanoparticlecomplex is prepared while together including a carrier during theprocess of forming nanoparticles as described above, there is anadvantage in that the adhesion between the carrier and the nanoparticlesand the dispersity are excellent.

When the adhesion between the carrier and the nanoparticles isexcellent, there is an advantage in that the durability may be improvedbecause the interaction between the nanoparticles and the carrier isimproved. Further, when the dispersity of nanoparticles is excellent onthe carrier, there is an effect in that the reactivity is improvedbecause the number of active points which may participate in reactionsis increased.

According to an exemplary embodiment of the present specification, theforming of the core particles includes performing reduction at atemperature of 120° C. or more and 220° C. or less. Specifically, theforming of the core particles may not include a separate reducing agent.Furthermore, within the temperature range, the polyol is changed into analdehyde, and may reduce the metal precursor.

According to an exemplary embodiment of the present specification, inthe forming of the core particles, the content of the core particles maybe 10 wt % or more and 50 wt % or less, or 10 wt % or more and 40 wt %or less, based on the total mass of the carrier and the core particles.Specifically, the content of the core particles may be 10 wt % or moreand 20 wt % or less, or 10 wt % or more and 15 wt % or less, based onthe total mass of the carrier and the core particles.

Forming of Core-Shell Nanoparticles

An exemplary embodiment of the present specification may include formingcore-shell nanoparticles by reducing an aqueous solution including metalcore particles supported on the carbon carrier, a Pt precursor, andwater at a temperature of 20° C. or more and 100° C. or less to form aPt shell on a portion or all of the metal core particle surface.

According to an exemplary embodiment of the present specification, theforming of the core-shell nanoparticles may include adjusting pH of theaqueous solution to 8 or more and 11 or less.

According to an exemplary embodiment of the present specification, inthe process of adjusting the pH, the pH may be adjusted by adding a basesolution. Specifically, the pH may be adjusted by adding a base solutionselected from the group consisting of sodium hydroxide (NaOH), bariumhydroxide (Ba(OH)₂), potassium hydroxide (KOH), calcium hydroxide(Ca(OH)₂), and lithium hydroxide (LiOH).

According to an exemplary embodiment of the present specification, theforming of the core-shell nanoparticles may include performing reductionat a temperature of 20° C. or more and 30° C. or less. Specifically,according to an exemplary embodiment of the present specification, sincethe forming of the core-shell nanoparticles may be performed in a normaltemperature range, there is an advantage in that high costs are notneeded to meet the process conditions.

According to an exemplary embodiment of the present specification, inthe forming of the core-shell nanoparticles, the Pt precursor may berepresented by the following Chemical Formula 1.PtA_(m)B_(n)  [Chemical Formula 1]

In Chemical Formula 1,

A is (NH₃), (CH₃NH₂), or (H₂O),

B is a monovalent anion,

m is 2, 4, or 6, and

n is any one integer of 1 to 7.

According to an exemplary embodiment of the present specification, B maybe NO₃ ⁻, NO₂ ⁻, OH⁻, F⁻, Cl⁻, Br⁻, or I⁻.

According to an exemplary embodiment of the present specification, thePt precursor may be Pt(NH₃)₄(NO₃)₂, Pt(NH₃)₄Cl₂, Pt(CH₃NH₂)₄(NO₃)₂,Pt(CH₃NH₂)₄Cl₂, Pt(H₂O)₄(NO₃)₂, or Pt(H₂O)₄Cl₂.

According to an exemplary embodiment of the present specification, inthe forming of the core-shell nanoparticles, the aqueous solution mayfurther include a reducing agent.

According to an exemplary embodiment of the present specification, thereducing agent is not particularly limited as long as the reducing agentis each a strong reducing agent having a standard reduction potential of−0.23 V or less, and has a reducing power which may reduce the dissolvedmetal ions to be precipitated as metal particles.

According to an exemplary embodiment of the present specification, thereducing agent may be each at least one selected from the groupconsisting of NaBH₄, NH₂NH₂, LiAlH₄, and LiBEt₃H.

An exemplary embodiment of the present specification may further includesubjecting the core particles to heat treatment at a temperature of 150°C. or more and 400° C. or less, or 180° C. or more and 300° C. or lessprior to the forming of the core-shell nanoparticles.

The subjecting of the core particles to heat treatment may contribute toimprovement in durability of the core-shell nanoparticles by subjectingcore particles to heat treatment prior to forming a shell portion toenhance the durability of the core particles. Furthermore, since thesubjecting of the core particles to heat treatment may also serve toremove the remaining solvent in the forming of the core particles,core-shell nanoparticles having excellent performance may be prepared.

For reference, when the heat treatment is performed after the forming ofthe core-shell nanoparticles, the structure of the shell is collapsed,and as a result, performance of the core-shell nanoparticles maysignificantly deteriorate.

According to an exemplary embodiment of the present specification, eachstep may not use a surfactant.

According to an exemplary embodiment of the present specification, eachstep of the preparation method does not use a surfactant, and thus hasan effect of reducing costs, and accordingly, the preparation method isalso advantageous in being favorable for mass production, and isadvantageous in terms of an eco-friendly process. When a surfactant isused, the surfactant surrounds the surface of the particle, so that apost-process of removing the surfactant is needed because there is aproblem in that the reactants are not easily accessed when thesurfactant is used in a catalyst reaction. Accordingly, when thesurfactant is not used, the preparation method has an effect of reducingcosts, and is also favorable for mass production because the process issimplified.

According to an exemplary embodiment of the present specification, thecore-shell nanoparticles may have a particle diameter of 3 nm or moreand 10 nm or less. Specifically, according to an exemplary embodiment ofthe present specification, the core-shell nanoparticles may have aparticle diameter of 3 nm or more and 7 nm or less.

According to an exemplary embodiment of the present specification, thecore particles may have a particle diameter of 2 nm or more and 9 nm orless. Specifically, according to an exemplary embodiment of the presentspecification, the core particles may have a particle diameter of 2 nmor more and 5 nm or less.

According to an exemplary embodiment of the present specification, thePt shell may have a thickness of 0.5 nm or more and 1.5 nm or less.Specifically, according to an exemplary embodiment of the presentspecification, the Pt shell may have a thickness of 0.7 nm or more and1.2 nm or less.

According to an exemplary embodiment of the present specification, thePt shell may have 1 or more and 4 or less Pt atomic layers.Specifically, according to an exemplary embodiment of the presentspecification, the Pt shell may have 2 or more and 3 or less Pt atomiclayers.

An exemplary embodiment of the present specification provides acarrier-nanoparticle complex prepared by the preparation method.

The carrier-nanoparticle complex according to an exemplary embodiment ofthe present specification may be used while replacing existingnanoparticles in the field in which nanoparticles may be generally used.

The carrier-nanoparticle complex according to an exemplary embodiment ofthe present specification has a much smaller size and a wider specificsurface area than the nanoparticles in the related art, and thus mayexhibit better activity than the nanoparticles in the related art.Specifically, the carrier-nanoparticle complex according to an exemplaryembodiment of the present specification may be used in the catalystfield.

Specifically, an exemplary embodiment of the present specificationprovides a membrane electrode assembly including an electrode catalystlayer which includes the carrier-nanoparticle complex and an electrolytemembrane.

Furthermore, an exemplary embodiment of the present specificationprovides a fuel cell including the membrane electrode assembly.

The fuel cell of the present specification includes a fuel cellgenerally known in the art. Specifically, the fuel cell may include: astack including the membrane electrode assembly and a separatorinterposed between the membrane electrode assemblies; a fuel supply partfor supplying fuel to the stack; and an oxidizing agent supply part forsupplying an oxidizing agent to the stack.

MODE FOR INVENTION

Hereinafter, the present specification will be described in detail withreference to Examples for specifically describing the presentspecification. However, the Examples according to the presentspecification may be modified in various forms, and it is notinterpreted that the scope of the present specification is limited tothe Examples described below. The Examples of the present specificationare provided to more completely explain the present specification to aperson with ordinary skill in the art.

[Example 1]—Preparation of Carrier-Nanoparticle Complex

3 g of polyethylene imine (PEI, Mw: 1,800) was dissolved in 600 ml ofwater, and then 720 mg of carbon black which had not been pre-treatedand 6 g of KNO₃ were added thereto, and the resulting mixture wasstirred for 24 hours. Thereafter, the mixture was washed with distilledwater and dried to obtain a carbon carrier coated with PEI. As a resultof an elemental analysis, the content of N in the carbon carrier was 2wt %, meaning that the carrier was smoothly coated with the PEI polymer.

After 0.096 mmol of Na₂PdCl₄, 0.065 mmol of CoCl₂, and 65 mg of thecarbon carrier coated with PEI were dissolved in 25 ml of ethyleneglycol, pH was adjusted to 11, and then the resulting solution wasstirred for a predetermined time. Moreover, after the temperature wasincreased up to 160° C., the solution was stirred for 3 hours, and thencooled to form Pd/Co core particles supported on the carbon carrier.

FIG. 1 illustrates an electron microscope photograph of Pd/Co coreparticles supported on a carbon carrier, which are prepared according toExample 1.

Moreover, after the Pd/Co core particles were washed with EtOH anddried, the resulting product was subjected to heat treatment at 220° C.for 1 hour, and then dispersed in 45 ml of distilled water, 0.096 mmolof Pt(NH₃)₄(NO₃)₂ was added thereto, pH was adjusted to 10, and then theresulting mixture was stirred for a predetermined time. Moreover, NaBH₄being a reducing agent was added thereto at room temperature, and theresulting mixture was reacted for a predetermined time, and then washedwith distilled water and dried to prepare a carrier-nanoparticle complexhaving core-shell nanoparticles supported on a carbon carrier.

FIG. 2 illustrates an electron microscope photograph of acarrier-nanoparticle complex in which core-shell nanoparticles aresupported on the carbon carrier, which is prepared according to Example1.

In Example 1, the Pd/Co core particles had a particle diameter of 2 nmto 5 nm, and the core-shell nanoparticles had a particle diameter of 3nm to 6 nm.

As a result of an ICP analysis of the core-shell nanoparticles of thecarrier-nanoparticle complex prepared according to Example 1, it wasshown that Pt, Pd, and Co were 20.6%, 9.4%, and 2.6%, respectively.

FIG. 3 illustrates component analysis results of the core-shellnanoparticles of the carrier-nanoparticle complex, which is preparedaccording to Example 1, by using STEM EDS.

[Example 2]—Preparation of Carrier-Nanoparticle Complex

3 g of polyethylene imine (PEI, Mw: 1,800) was dissolved in 600 ml ofwater, and then 720 mg of carbon black which had not been pre-treatedand 6 g of KNO₃ were added thereto, and the resulting mixture wasstirred for 24 hours. Thereafter, the mixture was washed with distilledwater and dried to obtain a carbon carrier coated with PEI.

After 0.096 mmol of Na₂PdCl₄, 0.11 mmol of CoCl₂, and 65 mg of thecarbon carrier coated with PEI were dissolved in 25 ml of ethyleneglycol, pH was adjusted to 11, and then the resulting solution wasstirred for a predetermined time. Moreover, after the temperature wasincreased up to 160° C., the solution was stirred for 3 hours, and thencooled to form Pd/Co core particles supported on the carbon carrier.

FIG. 4 illustrates an electron microscope photograph of Pd/Co coreparticles supported on a carbon carrier, which are prepared according toExample 2.

Moreover, after the Pd/Co core particles were washed with EtOH anddried, the resulting product was subjected to heat treatment at 220° C.for 1 hour, and then dispersed in 45 ml of distilled water, 0.16 mmol ofPt(NH₃)₄(NO₃)₂ was added thereto, pH was adjusted to 10, and then theresulting mixture was stirred for a predetermined time. Moreover, NaBH₄being a reducing agent was added thereto at room temperature, and theresulting mixture was reacted for a predetermined time, and then washedwith distilled water and dried to prepare a carrier-nanoparticle complexhaving core-shell nanoparticles supported on a carbon carrier.

FIG. 5 illustrates an electron microscope photograph of acarrier-nanoparticle complex in which core-shell nanoparticles aresupported on the carbon carrier, which is prepared according to Example2.

In Example 2, the core-shell nanoparticles had a particle diameter of 4nm to 7 nm.

As a result of an ICP analysis of the core-shell nanoparticles of thecarrier-nanoparticle complex prepared according to Example 2, it wasshown that Pt, Pd, and Co were 31.%, 8.7%, and 4.8%, respectively.

[Comparative Example 1]

A commercially available catalyst (JM40, Johnson Matthey Co., Ltd.) wasused.

[Comparative Example 2]—Preparation of Carrier-Nanoparticle Complex byUsing K₂PtCl₄ as Platinum Precursor

3 g of polyethylene imine (PEI, Mw: 1,800) was dissolved in 600 ml ofwater, and then 720 mg of carbon black which had not been pre-treatedand 6 g of KNO₃ were added thereto, and the resulting mixture wasstirred for 24 hours. Thereafter, the mixture was washed with distilledwater and dried to obtain a carbon carrier coated with PEI. As a resultof an elemental analysis, the content of N in the carbon carrier was 2wt %, meaning that the carrier was smoothly coated with the PEI polymer.

After 0.096 mmol of Na₂PdCl₄, 0.065 mmol of CoCl₂, and 65 mg of thecarbon carrier coated with PEI were dissolved in 25 ml of ethyleneglycol, pH was adjusted to 11, and then the resulting solution wasstirred for a predetermined time. Moreover, after the temperature wasincreased up to 160° C., the solution was stirred for 3 hours, and thencooled to form Pd/Co core particles supported on the carbon carrier.

Moreover, after the solution was washed with EtOH and dried, theresulting product was subjected to heat treatment at 220° C. for 1 hour,and then dispersed in 45 ml of distilled water, 0.16 mmol of K₂PtCl₄ wasadded thereto, pH was adjusted to 10, and then the resulting mixture wasstirred for a predetermined time. Moreover, NaBH₄ being a reducing agentwas added thereto at room temperature, and the resulting mixture wasreacted for a predetermined time, and then washed with distilled waterand dried to prepare a carrier-nanoparticle complex having core-shellnanoparticles supported on a carbon carrier.

FIG. 11 illustrates component analysis results of the core-shellnanoparticles of the carrier-nanoparticle complex, which is preparedaccording to Comparative Example 2, by using STEM EDS. Referring to FIG.11, it can be confirmed that the synthesized particles do not have acore-shell structure. Accordingly, it can be seen that a Pt shell may beformed only when the reaction is performed under the same cationic Ptprecursor and experimental conditions as in Examples 1 and 2.

[Experimental Example 1]—Evaluation of Catalytic Activity

30 mg of the carrier-nanoparticle complex prepared according to Example1, 1.8 ml of isopropyl alcohol, and 257 mg of a 5 wt % Nafion solutionwere mixed and dispersed well to prepare a catalyst ink. A Nafionmembrane (NR 211) was coated with the prepared catalyst ink by using aspray apparatus. After drying, the membrane was heated and compressed at140° C. for 2 minutes and 30 seconds to manufacture a membrane electrodeassembly.

By using the carrier-nanoparticle complex prepared according to Example2, a membrane electrode assembly was manufactured by the method asdescribed above.

Further, as Comparative Example 1, by using a commercially availablecatalyst (JM40, Johnson Matthey Co., Ltd.), a membrane electrodeassembly was manufactured by the method as described above.

Furthermore, by using a membrane electrode assembly sample with a sizeof 2.5 cm×2.5 cm, H₂/Air was supplied under a 100% humidified condition,and the performances of a single cell were measured under a 75° C.atmosphere. The performance evaluation results of a membrane electrodeassembly using the carrier-nanoparticle complexes according to Examples1 and 2 and a membrane electrode assembly using the commerciallyavailable catalyst (JM40, Johnson Matthey Co., Ltd.) are shown in thefollowing Table 1.

TABLE 1 Pt + Pd mass Pt mass per Current Activity per unit area unitarea density per mass (mgPtPd/cm²) (mgPt/cm²) (A/cm²) (A/mgPt)Comparative 0.4 0.4 1.107 2.77 Example 1 Example 1 0.273 0.15 0.974 6.5Example 2 0.49 0.32 1.046 3.27

FIG. 6 illustrates a current density-voltage graph of ComparativeExample 1, Example 1, and Example 2.

Furthermore, FIG. 7 is a normalization graph based on the amount of Ptper unit area in the graph in FIG. 6.

According to FIG. 7 and Table 1, even though the amount of Pt per unitarea is small, the carrier-nanoparticle complex according to the Exampleexhibits a performance which is equivalent to that of the commerciallyavailable catalyst (Comparative Example 1), which uses 0.4 mgPt per unitarea. That is, it can be seen that Pt is present only in the shell, andas a result, the Example may exhibit an equivalent performance eventhough Pt is used in a small amount, and exhibits high Pt activity ascompared to Comparative Example 1 in which the commercially availablecatalyst is used.

[Experimental Example 2]—Evaluation of Catalyst Durability

The evaluation of the catalyst durability was carried out in a half cellsystem. As an electrode, a 3-electrode system, that is, a referenceelectrode, a counter electrode, and a working electrode were used, thereference electrode was Ag/AgCl, and as an electrolyte, a 0.5 M sulfuricacid solution or a 0.1 M perchloric acid solution was used.

Furthermore, scanning was performed 1000 times from −0.2 V to 1.0 V byusing cyclic voltammetry, and the scan rate was 20 mV/s.

A catalyst ink was prepared by mixing 2 mg of the carrier-nanoparticlecomplex prepared according to Example 1 or a commercially availablecatalyst (JM40, Johnson Matthey Co., Ltd.), 8 μl of 5% Nafion, 1.6 ml ofEtOH, and 0.4 ml of H₂O, and dispersing the resulting mixture by usingan ultrasonic washing machine for 1 hour, and then the above-describedelectrode was coated with 20 μl of the catalyst ink, and the coating wasdried. The amount of catalyst coated on the electrode was about 20 μg,and the area of the electrode was 0.196 cm².

FIG. 8 illustrates a graph of the catalyst durability evaluationperformed by cyclic voltammetry in Example 1 and Comparative Example 1.The y-axis in FIG. 8 is an electric chemical surface area (ECSA), andmeans an active surface area of platinum, which is calculated by usingthe amount of hydrogen adsorbed onto the surface of platinum.Specifically, the ECSA may be calculated by the following Equation 1.ECSA=Q/{(210 μC/cm²Pt)×M(g_(pt)/cm²)}  [Equation 1]

In Equation 1, Q means a quantity of electric charge (C/cm²), and Mmeans an amount of platinum per area of an electrode (gPt/cm²).

Furthermore, the following Table 2 exhibits the catalytic activityaccording to the cycle of cyclic voltammetry.

TABLE 2 JM 40 Example 1   0 cycle 76.97 m²/cm² 73.43 m²/cm² 1000 cycle23.78 m²/cm² 36.37 m²/cm² Rate in decrease 69% 50%

According to FIG. 8 and Table 2, it can be seen that thecarrier-nanoparticle complex according to the Example has a low rate indecrease of activity according the increase in number of cyclesaccording to the cyclic voltammetry. That is, it can be seen that thecarrier-nanoparticle complex according to the Example exhibits excellentdurability.

[Reference Example 1]—Heat Treatment after Formation of Core-Shell

3 g of polyethylene imine (PEI, Mw: 1,800) was dissolved in 600 ml ofwater, and then 720 mg of carbon black which had not been pre-treatedand 6 g of KNO₃ were added thereto, and the resulting mixture wasstirred for 24 hours. Thereafter, the mixture was washed with distilledwater and dried to obtain a carbon carrier coated with PEI.

After 0.096 mmol of Na₂PdCl₄, 0.11 mmol of CoCl₂, and 65 mg of thecarbon carrier coated with PEI were dissolved in 25 ml of ethyleneglycol, pH was adjusted to 11, and then the resulting solution wasstirred for a predetermined time. Moreover, after the temperature wasincreased up to 160° C., the solution was stirred for 3 hours, and thencooled to form Pd/Co core particles supported on the carbon carrier.

Moreover, after the Pd/Co core particles were washed with EtOH anddried, the resulting product was dispersed in 45 ml of distilled water,0.16 mmol of Pt(NH₃)₄(NO₃)₂ was added thereto, pH was adjusted to 10,and then the resulting mixture was stirred for a predetermined time.Moreover, NaBH₄ being a reducing agent was added thereto at roomtemperature, and the resulting mixture was reacted for a predeterminedtime, and then washed with distilled water and dried, and then subjectedto heat treatment at 220° C. for 1 hour to prepare acarrier-nanoparticle complex having core-shell nanoparticles supportedon a carbon carrier.

FIG. 9 illustrates XRD results of Example 2 and Reference Example 1.According to FIG. 9, it can be seen that the case of Example 2 in whichcore particles were subjected to heat treatment, and then a Pt shell wassynthesized coincided with the XRD peak pattern of Pt, and the case ofReference Example 1 in which a Pt shell was synthesized, and thensubjected to heat treatment coincided with the XRD peak pattern of aCoPt₃ alloy. This means that in the case of Reference Example 1, themetals of the core and shell are present in the form of an alloy on thesurface thereof during the heat treatment process, and the structure ofthe Pt shell is collapsed.

[Reference Example 2]—Coating of Carrier with Polymer Having SkeletonIncluding Cyclic Molecule

2.5 g of polydiallyl dimethyl ammonium chloride (PDDA, Mw: 100,000 to200,000) was dissolved in 50 ml of water, and then 720 mg of carbonblack which had not been pre-treated and 6 g of KNO₃ were added thereto,and the resulting mixture was stirred for 24 hours. Thereafter, themixture was washed with distilled water and dried to obtain a carboncarrier coated with PEI.

After 0.096 mmol of Na₂PdCl₄, 0.11 mmol of CoCl₂, and 65 mg of thecarbon carrier coated with PEI were dissolved in 25 ml of ethyleneglycol, pH was adjusted to 11, and then the resulting solution wasstirred for a predetermined time. Moreover, after the temperature wasincreased up to 160° C., the solution was stirred for 3 hours, and thencooled to form Pd/Co core particles supported on the carbon carrier.

Moreover, after the Pd/Co core particles were washed with EtOH anddried, the resulting product was subjected to heat treatment at 220° C.for 1 hour, and then dispersed in 45 ml of distilled water, 0.16 mmol ofPt(NH₃)₄(NO₃)₂ was added thereto, pH was adjusted to 10, and then theresulting mixture was stirred for a predetermined time. Moreover, NaBH₄being a reducing agent was added thereto at room temperature, and theresulting mixture was reacted for a predetermined time, and then washedwith distilled water and dried to prepare a carrier-nanoparticle complexhaving core-shell nanoparticles supported on a carbon carrier.

A catalytic activity evaluation was performed on thecarrier-nanoparticle complex prepared as described above in the samemanner as in Experimental Example 1, and the result according to theevaluation is illustrated in FIG. 10. Specifically, FIG. 10 illustratesa current density-voltage graph of Reference Example 2. According toFIG. 10, it can be seen that the current density of Reference Example 2at 0.6 V is 0.53 A/cm², which is much lower than those of Examples 1 and2. From the result, it can be seen that the case where a carrier iscoated with a polymer having a skeleton including a cyclic moleculeshows a lower performance than that of a polymer having a straight orbranched skeleton.

The invention claimed is:
 1. A method for preparing acarrier-nanoparticle complex, the method comprising: preparing a carboncarrier having a portion or all of a surface of the carbon carriercoated with a polymer comprising a cationic functional group; formingcore particles by reducing a solution comprising one or more metalprecursors, the carbon carrier, and a polyol at a temperature of 120° C.or more and 220° C. or less to form metal core particles supported onthe carbon carrier; and forming core-shell nanoparticles by reducing anaqueous solution consisting of the metal core particles supported on thecarbon carrier, a Pt precursor, and water at a temperature of 20° C. ormore and 100° C. or less to form a Pt shell on a portion or all of themetal core particle surface, wherein the core-shell nanoparticles aresupported on the carbon carrier, and the Pt precursor is represented bythe following Chemical Formula 1:PtA_(m)B_(n)  [Chemical Formula 1] in Chemical Formula 1, A is (NH₃),(CH₃NH₂), or (H₂O), B is a monovalent anion, m is 2, 4, or 6, and n isany one integer of 1 to
 7. 2. The method of claim 1, wherein the formingof the core particles includes adjusting pH of the solution to 9 or moreand 11 or less.
 3. The method of claim 1, wherein the forming of thecore-shell nanoparticles includes performing reduction at a temperatureof 20° C. or more and 30° C. or less.
 4. The method of claim 1, whereinthe polymer comprising the cationic functional group comprises one ormore functional groups selected from a group consisting of an aminegroup, an imine group, and a phosphine group.
 5. The method of claim 1,wherein the core-shell nanoparticles form a bonding structure with thecationic functional group.
 6. The method of claim 1, wherein the polymercomprising the cationic functional group has a weight average molecularweight of 500 g/mol or more and 1,000,000 g/mol or less.
 7. The methodof claim 1, wherein the polymer comprising the cationic functional groupis a polymer in which a straight or branched hydrocarbon chain issubstituted with the cationic functional group.
 8. The method of claim1, wherein the metal core particles are bonded to cations of the polymercomprising the cationic functional group.
 9. The method of claim 1,wherein in the forming of the core particles, the metal precursor is aprecursor of one or more metals selected from a group consisting of Co,Ni, Fe, Pd, Ru, Cr, and Cu.
 10. The method of claim 1, wherein B is NO₃⁻, NO₂ ⁻, OH⁻, F⁻, Cl⁻, Br⁻, or I⁻.
 11. The method of claim 1, whereinin the forming of the core-shell nanoparticles, the Pt precursor isselected from the group consisting of Pt(NH₃)₄(NO₃)₂, Pt(NH₃)₄Cl₂,Pt(CH₃NH₂)₄(NO₃)₂, Pt(CH₃NH₂)₄Cl₂, Pt(H₂O)₄(NO₃)₂, and Pt(H₂O)₄Cl₂. 12.The method of claim 1, further comprising: subjecting the core particlesto heat treatment at a temperature of 150° C. or more and 400° C. orless prior to the forming of the core-shell nanoparticles.
 13. Themethod of claim 1, wherein each step does not use a surfactant.
 14. Themethod of claim 1, wherein the core-shell nanoparticles have a particlediameter of 3 nm or more and 10 nm or less.
 15. A carrier-nanoparticlecomplex prepared by the method according to claim
 1. 16. A membraneelectrode assembly comprising: an electrode catalyst layer whichcomprises the carrier-nanoparticle complex according to claim 15; and anelectrolyte membrane.
 17. A fuel cell comprising: the membrane electrodeassembly according to claim 16.